Electric safety-fuse.



T. E. MURRAY.

ELECTRIC SAFETY FUSE. APPLIUATION FILED JULY 18, 1907.

920,61 3, Patented May 4, 1909.

a A! T u: "n" g I WJTNESSES. INVENTOR C: g HQ BY /j flfi W ATTORNER covered that the problem of preventing rupmahle,inexpensive, proof against moisture THOMAS E. MURRAY, OF NEW YORK, N.

ELEo'rRIc SAFETY-FUSE.

Specification of'Letters Patent.

Patented May 4, 1909.

Application filed Ju1y 18, 1907. Serial No. 384,436.

T 0 all whom it mag concern: 1 Be it known that I, THOMAS E. MURRAY, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented a certain new and useful Improvement in Electric Safety- Fuses, of which the following is a specification. K

The invention relates to' fuses.

The advantages of making the containing tubes of electric safety fusesof porcelain, glass or other fictile or vitreous material are that said material is insulating, non-inflamelectric safety and easily and cheaply molded. On the other hand, it is fragile, and especially so under the sudden shock of the explosion of the fuse inclosed within it. Attempts have been made to meet this difiiculty by providing escape ducts for the suddenly generated of explosion, or by the use of filling materials which would chemically combine with such gases and establish new paths of low resistance, or by providing auxiliary conductors or by-passes outside the fuse, or by making the porcelain or glass envelop in sections which it was supposed might yield at the joints, or by doing away with the desired material altogether and substituting paper or fibrous compounds; thus in the last case, for the sake of toughness, sacrificing the other desirable qualities above noted and at the sametimc incurring the dangers due to infiammability of the material. I have disture of fictile or vitreous tubes in such conditions can be solved by dampening the explosive vibration before it gets to the tube wall, and that this can be done if the fuse wire or strip within the tube is everywhere embedded in some inert and refractory material capable of acting as such a damper, and thus of protecting the tube from the direct shock. The breakage of the material of the tube is due not to continued strain like gas pressure in the bore of a gun, but to the immensely rapid jar which, especially if concentrated at some small portion of the tube, forces the molecules asunder beyond. the range of their mutual cohesive attraction. I have found that when this shock is lengthened out, retarded, so to speak, the molecules apparently ettime to adqustv themselves to it and withstand what now becomes less a shock than a strain. All that is necessary, therefore, is to see to it that there is enough dampening material inter osed between fuse wire and tubeto effectthls retardation. If none is present the porcelain or glass will break; if suflicient is resent the porcelain or glass will not brea and that is the test.

I am aware that fuse wires have been disposed in glass tubes filled over portions of their length with so-called non-conducting material, there being elsewhere nothing but air space between fuse wire and tube. There is no possible suggestmn of my principle in such a structure for the reason that to leave a part of the tube without dampening protection is even worse than to expose'thc whole of it; for the shock will localize at the unprotected portion, and besides the mere fact that any of the tube is thus left unprotected is to-negative conclusively the perception of said principle. So also the presence of any one of the expedients above noted for avoiding the effects of the explosion, also negatives the inference of recognition of thatprin'ciple, because none of them in any sense embodies it. On the contrary they each involve substitution of an essentially different principle I create no escape duct for gases, I form no by path for the liberated energy, I neither combine the metal ofthe fuse chemically with the ingredients of the tube filling, nor rely upon any dissemination of that metal through a comminnted mass to produce a new path of low resistance. All of thme expedients are too slow. The shock overcomes the molecular cohesion of the glass beyond its power to react before these things can get into action. Hence the need of retarding the propagation of the shock vibration by a medium interposed between the explosive focus and the comparatively fragile wall to be rotected.

In the accompanying rawingsFigure 1 is a side elevationof my improved fuse showing a part in longitudinal section on the line of Fig. 2. Fig. 2 is an end View.

Similar letters of reference indicate like parts.

A is a tube integrally formed of porcelain. At the ends of saidtube arecaps B, C preferably made by spinning up sheets of brass or other metal.

D is the fuse wire or strip, which may be of zincfsecured at its ends to the brass connecting pieces E, E, which pieces fit in openings in the caps B, C.

Thewhole interior of the tube A is filled with non-combustible material G, such as.

plaster, pr asbestos in suficient quantity to dampen the explosion of the blowing fuse and to retard its period of action upon the glass or porcelain of the tube. The density of the mass is immaterial so long as the desired result is produced. With some substances such as mixtures of magnesia and asbestos the interposed material may be substantially coherent and solid. With others suchas plaster it may be in a powder an loose. In some ,cases, the interposed material may, as already stated, completely fill the tube; in others it may be of less thickness and thus, if sutficiently coherent, may

form a sleeve surrounding the fuse. But in all cases, there mustnot be free air space between the fuse proper and the tube well, anywhere. The wall must be directly shielded everywhereby the interposed material.

In order to insure the complete embedding of the active fuse, the connecting pieces E, F, are provided, and the fuse proper is,

therefore, preferably not to be connected directly with the metal caps. These caps are preferably struck up from sheet metal to avoid joints, and the circuit terminals are connected to them in any suitable way.

'The term fictile material in the claim is intended toinclude'not merely material made by -the potter, such as porcelain, but also glass and like vitreous material. liable to be ruptured by sudden shock.

I claim In a safety fuse, a fusible strip, a tube integrally formed of fictilematerial inclosing said strip and a body of inert and refractory material everywhere interposed between said'strip and said tube, and constructed to dampen or retard the vibrations due to sudden shock of explosion and thereby to prevent rupture of said tube. I

'In testimony whereof I have afiixed my signature in presence of two witnesses.

GERTRUDE T. PORTER, MAUDE A.YROGERS. 

